If images are taken of the heart by means of nuclear medical investigation methods such as, for example, PET (Positron Emission Tomography) and SPECT (Single Positron Emission Computer Tomography), this involves long acquisition times typically lasting a few minutes (as in PET) and up to more than 20 minutes (in SPECT). The resulting data set therefore represents a time-related averaging over all the cardiac phases and the cardiac motion therefore appears blurred.
Furthermore, DE 102 31 061 A1 discloses a method for imaging, onto a reference time, three-dimensional image data recorded by means of a first imaging method (PET) and containing motion artifacts, and for compensating for the motion artifacts. To achieve this, a second image generation method (CT) is used, with which a ti me series of image data is recorded, from which motion fields are determined that are used to compensate for the motion artifacts from the first image generation method. The first image generation method claimed in DE 102 31 061 A1 produces only a fuzzy and blurred image, however. This blurring can restrict the usability of the data set for diagnosis.
In order to avoid this effect, an ECG gating can be applied. In an ECG gating, an ECG is taken at the same time as the image data are recorded. ECG gating is based on the fact that the cardiac cycle is repeated. The image data that are recorded during equal intervals of the cardiac cycle are therefore coordinated. Thus a time series of three-dimensional image data is obtained, wherein said image data have always been recorded within a certain interval in the cardiac cycle. The series is achieved by juxtaposing the sequence of images for the respective intervals in the cardiac cycle.
What is then obtained is a plurality of images, with each respective image corresponding to a specific phase of the cardiac cycle. The cardiac motion should always remain the same and therefore no substantial motion blurring should occur in each of the respective individual images.